To compensate for channel distortion and fading when demodulating received signals, reception devices require improved demodulation accuracy and assured tracking of rapid channel changes. Techniques for this purpose include equalization, which corrects the phase and amplitude of the received signal, and diversity, which improves reception performance by combining signals from multiple antennas.
A known method of equalization is to estimate the channel by using a known signal added onto the received signal as a reference signal and use the channel estimate signal to correct the received signal. Another known method of equalization (patent references 1 and 2 for example) first equalizes a data interval other than the known signal, estimates the channel by using the re-encoded signal as a reference signal, and then corrects the received signal. These methods can compensate for channel distortion.
A known diversity technique (patent references 2 and 3 for example) is the maximum ratio combining technique that aligns the phases of the signals (also referred to below as branches) received at the different antennas, weights the signals according to their received signal levels, and then combines them, thereby maximizing the carrier power to noise power ratio (also referred to below as the ‘C/N’). Another proposed diversity technique (patent reference 4 for example) detects an equivalent C/N, input power, and delay profile from the demodulated signal of each branch and controls their combining ratios according to these factors in order to improve reception performance.